Copy records of one table into another using Update statement

Question

Supposing I have 2 tables test and test1.
Test has columns col1 and col2. and test1 has only one table col1.
select * from test returns:
COL1 COL2
a
b
c
d
e
select * from test1 returns
COL1
p
q
r
s
t
Suppose i want to copy values of test1.col1 to test.col2 so tht final result of
select * from test should be
COL1 COL2
a p
b q
c r
d s
e t
I found a query in the OCP introduction book:
update test set col2=(select col1 from test11)
this works fine only when we have a single record in test1 table but fails otherwise.
how can this be achieved using the update statement ?

Answer 1

SQL> desc test
Name Null? Type
COL1 VARCHAR2(10)
COL2 VARCHAR2(30)
SQL> desc test1
Name Null? Type
COL1 VARCHAR2(10)
SQL> insert into test values ('a','');
1 row created.
SQL> insert into test values ('b','');
1 row created.
SQL> insert into test values ('c','');
1 row created.
SQL> insert into test values ('d','');
1 row created.
SQL> insert into test1 values ('e');
1 row created.
SQL> insert into test1 values ('f');
1 row created.
SQL> insert into test1 values ('g');
1 row created.
SQL> insert into test1 values ('h');
1 row created.
SQL> commit;
Commit complete.
SQL> ed
Wrote file afiedt.buf
1 select a.col1, b.col1, a.rn from
2 (select row_number() over (order by col1) rn, col1 from test) a,
3 (select row_number() over (order by col1) rn, col1 from test1) b
4* where a.rn = b.rn
SQL> /
COL1 COL1 RN
a e 1
b f 2
c g 3
d h 4
SQL> ed
Wrote file afiedt.buf
1 update test set col1 =
2 (
3 select forupd from (
4 select a.col1, b.col1 test1col, a.col1||' '||b.col1 forupd, a.rn from
5 (select row_number() over (order by col1) rn, col1 from test) a,
6 (select row_number() over (order by col1) rn, col1 from test1) b
7 where a.rn = b.rn
8* ) z where z.col1 = test.col1)
SQL> /
4 rows updated.
SQL> commit;
Commit complete.
SQL> select * from test;
COL1 COL2
a e
b f
c g
d h
SQL>
This will work only if you have the same number of lines in COL1 in both tables. If you have different number of lines, then you need to code more at join (outer, inner).
But for complicated cases, please post sample data.
Michael
PS: And supossing that the values are distinct in TEST table. Else update will fail, because more rows will be retrived.
If more values in TEST table in COL1, then you need to assign a row number on TEST also, and in WHERE of query you need to place one more join condition:
something like:
8* ) z where z.col1 = test.col1
and z.rn = test.rn)
SQL> /
But as i said, get more specifications.
Message was edited by:
kjt
Added the PS.